How is the power of a battery calculated?

Using a battery with a voltage of 12 volts but less than 20 ampere-hours may not be sufficient to power the device.

20ah refers to the capacity of the battery, not its power. When the current is constant, the greater the capacity, the longer the duration for which power can be supplied.

The meaning of 20ah is that when the battery outputs a current of 20 amps, it can be used for 1 hour. It can also be interpreted as when the battery outputs a current of 2 amps, it can be used for 10 hours, etc. That is, the product of the current and time is 20.

When the equipment requires a 20ah high-power battery to operate, this indicates that the device has a relatively large working current. A small-capacity battery may not be able to withstand such a high current. If a small-capacity battery can handle the driving current of the equipment, then it can operate. It's like trying to power an electric bicycle by connecting together a dozen seven-cell batteries - it won't work.

This refers to the capacity of the battery, not the power. It indicates the duration for which a certain power-consuming appliance can operate. The length of the operating time depends on the power of the appliance.

In addition to the 100Ah capacity, the battery also needs to know the voltage level. This battery can operate for 1 hour at a current of 100 amperes. The specific power depends on the voltage of the battery. For example, for a 12V battery, if the working current is 100 amperes, it can power a 1200-watt appliance for one hour. If the current is 10 amperes, it can operate for 10 hours. The exact working time depends on the current used and the voltage of the battery.

Batteries do not measure power; they measure "milliampere-hours", which refers to the duration of discharge in milliamps. This is the battery's electrical capacity. The voltage of a new ordinary 5-volt dry battery is 1.5 volts, and its internal resistance is approximately 1 ohm. The voltage drops during discharge. If the discharge current reaches 500 milliamps, a voltage drop of 0.5 volts will occur, and the output voltage will only be 1 volt. The greater the discharge current, the smaller the total discharge capacity and the shorter the lifespan. The continuous discharge lifespan is even shorter.

Let me explain it to you from the perspective of the organization.

The unit of power is watt (W), which is given by P = UI. 1W = 1V.A (one watt is equal to one volt-ampere)

Battery capacity mA.h (milliampere-hours)

It is obvious that these two parts are different.

Look for the connection further:

Unit of electrical energy and work: Joule (J)

From W = Pt

It is known that: 1J = 1W.s = 1V.A.s (one joule is equal to one volt-ampere-second)

If the voltage of the battery is known, multiply it by the battery capacity and see what you get: V.mA.h

In fact, it is essentially the same as the unit of electrical energy. Let's do the conversion:

1V.mA.h = 1V * 10^-3A * 3600s = 3.6V.A.s = 3.6J

A battery is an energy storage component. There is no concept of power. It has a rated capacity, measured in watt-hours (wh). The power can be calculated by multiplying the voltage by the capacity. For example, Redmi.

"12V12AH battery" does not mean that its power is 12 multiplied by 12 equals 144 watts!

"12V12AH battery" refers to the capacity of this battery. That is, the rated working voltage of this battery is 12 volts. If the discharge current is 1 ampere, it can be used for 12 hours; if the discharge current is 0.1 ampere, it can be used for 120 hours; if the discharge current is 0.5 ampere, it can be used for 24 hours; and so on.

The battery also has an indicator, which is the rated working current. Generally, the usage should not exceed the rated working current; otherwise, the battery's lifespan will be shorter. [If the current is too high, the plates inside may flake off easily].

"Connect the 300W lamp" requires that the discharge current of the battery be: I = P/U = 300/12 = 25 amperes. If it does not exceed the battery's rated current, it can be used; if it exceeds, even by a lot, it cannot be used.

If possible, the approximate usable time would be: 12 ampere-hours / 25 ampere-hours = 0.48 hours. [Taking into account the losses in the inverter itself, the battery itself, and the circuit, it would be shorter than 0.48 hours.]

"MAh" is the unit for battery capacity. Its Chinese name is milliampere-hour (When measuring large-capacity batteries such as lead-acid batteries, for convenience, "Ah" is commonly used to represent it, and its Chinese name is ampere-hour).

1mAh = 0.001 ampere * 3600 seconds = 3.6 ampere-seconds = 3.6 coulombs

2. Coulomb is a unit of electric charge. Coulomb is not a basic unit of the International System of Units, but rather a derived unit. 1 Coulomb = 1 Ampere-second.

The amount of electric charge transported by a current in 1 second is 1C, which is equivalent to 1A·s.

3. Power calculation formula for electrical power: P = UI. The unit of P is watts (W); in a pure resistive circuit, by substituting U = IR from Ohm's Law into P = UI, we can also obtain: P = I * IR = (U * U) / R

1. The most direct algorithm:

1. First, obtain the current of the electrical equipment.

2. Then, divide the battery capacity by the current of the electrical device, and the result will be the duration of usage.

For example:

A battery with a capacity of 3000mAh and a rated voltage of 5V supplies power to an electrical device with a power consumption of 2.5W and a voltage of 5V. The theoretical usage duration of this battery is:

I = P / U => 2.5w / 5v => 0.5A => 500MA

3000mAh means that a current of 3000MA can discharge the battery for one hour.

3000 divided by 500 equals 6 hours.

II. Using the Coulomb algorithm for charge quantity

C = IS => 3A * 3600s => 10800 coulombs (charge quantity)

10800c * 5v = 54000w of electrical energy

54000w / 2.5w = 21600 / 3600 = 6 h